Hot Flushes in the Menopause

Why do they happen?

A hot flush is the response of the brain's temperature centre to the withdrawal of oestrogen. There is an important detail here: the problem is not that oestrogen is low, but that it was present and has been withdrawn. Oestrogen is also low in girls before puberty, and they do not have hot flushes.

When oestrogen is withdrawn, the range of temperature the body finds comfortable narrows. A rise in internal temperature that would normally go unnoticed is now read by the brain as "too hot". To cool the body quickly the brain widens the blood vessels in the skin — which is why there is sudden redness and heat in the face and upper chest. Heavy sweating follows. Because the body loses heat rapidly as the sweat evaporates, this is often followed by chills, shivering and sometimes a feeling of anxiety.

How common, and how long?

• 70-80% of women going through the menopausal transition have hot flushes.
• Between a quarter and a third of them describe the symptom as severe enough to disrupt daily life and sleep.
• Yet only 20-30% seek medical help for it.

Nor do they always stop with age: around 40% of women over 60 still have hot flushes, and 8% of women who are more than 20 years past the menopause still experience them.

Duration also differs by ethnicity: in SWAN the longest median duration was in African-American women (10.1 years) and the shortest in Chinese and Hispanic women (about 5 years).

What makes them worse?

• Weight and abdominal fat: increases both frequency and severity.
• Smoking: triggers and worsens flushes, and also brings the menopause forward.
• Being inactive: flushes are more frequent and more severe in women who do not exercise regularly.
• Surgical menopause: when both ovaries are removed, hormone levels fall abruptly rather than gradually, and symptoms are considerably more severe.
• Food and drink: alcohol, caffeine, spicy food and very hot food can trigger an episode.
• Stress and anxiety: the relationship runs both ways — stress triggers episodes, and frequent flushes deepen anxiety and low mood.

Non-hormonal approaches: which ones have evidence?

A great deal is recommended under this heading, but most of it has weak scientific support. The guidelines draw the line as follows:

Those with evidence

• Cognitive behavioural therapy: the non-hormonal approach with the strongest evidence. It does not abolish the episodes; it significantly reduces how distressing and intrusive they feel, and improves sleep and quality of life. Menopause-specific programmes of 4-6 sessions are used.
• Clinical hypnosis: in studies it reduced both the frequency and the severity of flushes markedly.
• Weight loss: there is supporting evidence that it may reduce symptoms in women who are overweight.

Those where evidence did not emerge

• Exercise and yoga: extremely valuable for heart, muscle and bone health — but randomised trials have not shown a direct benefit over placebo for the flushes themselves. Because internal temperature rises during exercise, it may even trigger an episode temporarily.
• Paced breathing: not found superior to placebo, and therefore not recommended by menopause societies for this symptom.
• Herbal supplements: black cohosh, St John's wort, dong quai, ginseng, wild yam, flaxseed and acupuncture have not been shown to be superior to placebo. For soy isoflavones a modest reduction of about 25% has been reported once the placebo effect is removed.

How effective is hormone therapy?

Hormone therapy is the most effective option for flushes and night sweats. The evidence shows that it:

• reduces the frequency of episodes by about 75% compared with placebo;
• completely resolves the symptom in about 80% of women at standard doses, and markedly reduces frequency and severity in the rest;
• begins to take effect within the first two weeks, reaching its maximum at around week 12;
• is followed by a return of symptoms in 50-87% of women when it is stopped.

Who hormone therapy is suitable for, its risks and the importance of timing are a separate subject — see menopoz tedavisi and the long-term risks of the menopause.